1. Field of the Invention
The present invention relates to a method of production of peeling layer paste used for production of a multilayer ceramic capacitor or other multilayer electronic device and a method of production of a multilayer type electronic device using the peeling layer paste.
2. Description of the Related Art
In recent years, due to the increasingly smaller sizes of electronic apparatuses, multilayer ceramic capacitors and other multilayer electronic devices have become increasingly compact in size and sophisticated in performance. The thicknesses of the interlayer dielectric layers of multilayer electronic devices (dielectric layers sandwiched between pairs of internal electrodes) have become 1 μm or less—enabling over 800 stacked layers. In the process of production of such electronic devices, the thicknesses of the green sheets able to form the dielectric layers after firing have become extremely thin (usually 1.5 μm or less), so at the time of formation of the electrode layers by the printing method, the solvent of the electrode layer paste causes the green sheets to dissolve, that is, the so-called “sheet attack” phenomenon becomes a problem. This sheet attack phenomenon leads directly to defects of the green sheets and short-circuit defects, so is a problem which absolutely must be solved for making the layers thinner.
To eliminate this sheet attack, Japanese Patent Publication (A) No. 63-51616, Japanese Patent Publication (A) No. 3-250612, and Japanese Patent Publication (A) No. 7-312326 propose forming an electrode layer paste on a support film in a predetermined pattern, then drying it so as to separately prepare a dry electrode layer, then transferring this dry electrode layer to the surface of a green sheet or the surface of a laminate of green sheets so as to transfer the predetermined pattern of the electrode layer.
However, the technology of Japanese Patent Publication (A) No. 63-51616, Japanese Patent Publication (A) No. 3-250612, and Japanese Patent Publication (A) No. 7-312326 had the problem of a difficulty of peeling off the predetermined pattern of the electrode layer from the support film. Therefore, the inventors proposed technology for forming a peeling layer between a support film and a predetermined pattern of an electrode layer so as to improve the peelability of the electrode layer (see Japanese Patent Publication (A) No. 2003-197457).
However, generally, this type of peeling layer has to be formed extremely thin. Specifically, it is preferably formed to a thickness of 0.2 μm or less. This type of peeling layer is not provided for the purpose of functioning as a dielectric layer after firing and is only provided for the purpose of facilitating formation and peeling of the predetermined pattern of the electrode layer. When forming the peeling layer thick, the active thickness of the interlayer dielectric layer after firing ends up being reduced, so this is disadvantageous for raising the capacity. To make the peeling layer extremely thin, it is necessary to cause ceramic powder having a particle size smaller than the thickness of the peeling layer to homogeneously disperse in the paste for formation of the peeling layer.
However, when using extremely fine ceramic powder to prepare a peeling layer paste by the conventional method, during preparation of the paste, the ceramic powder sometimes partially coagulates. If using peeling layer paste containing partially coagulated ceramic powder to form a peeling layer, the thickness of the peeling layer tends to become thick in parts and therefore a uniform peeling layer becomes hard to form. Even if forming this peeling layer with a predetermined pattern of an electrode layer, the density and surface conditions of the electrode coating deteriorate, so it is difficult to make full use of the merits of a dry electrode.
The peeling layer is formed by coating or drying a peeling layer paste using a bar coater, microgravure coater, extrusion coater, or other device, but to reduce the coated thickness of the peeling layer paste so that the thickness of the final peeling layer becomes 0.2 μm or less, the amount of paste supplied to the coating device has to be made smaller and the nonvolatile concentration of the paste has to be made lower. Further, as the nonvolatile ingredients of the peeling layer paste, the ingredients other than the dispersion medium (solvent) may be considered. Specifically, it is necessary to use a paste with a nonvolatile concentration of 15 wt % or less, but a paste (or slurry) with such an extremely low nonvolatile concentration is hard to stably produce by a single dispersion process. Therefore, it is necessary to repeatedly perform the process of dispersion and dilution of slurry to gradually lower the nonvolatile concentration.
However, at the stage of diluting the slurry, the coagulation phenomenon called “solvent shock” sometimes occurs. There was a problem in high pressure dispersion of a slurry with an extremely low nonvolatile concentration.
Further, Japanese Patent No. 3387455 proposes a method of high pressure dispersion of a green sheet paste used for forming a green sheet for forming a dielectric layer after firing. Specifically, it proposes combining the medium-type dispersion method using pebbles, beads, or another dispersion medium and the high pressure dispersion method of dispersion at a pressure of 100 kg/cm2 or more to cause the ceramic powder to disperse in the paste. Japanese Patent No. 3387455 deals with paste for forming a green sheet of several μm at the thinest, so the content of the binder contained in the paste is set small. This is because if the amount of binder in the green sheet paste becomes large, the content of the ceramic powder becomes smaller relative to this and cracks and other problems occur at the time of molding or removal of the binder.
As opposed to this, if the amount of binder ends up becoming smaller in a peeling layer paste not for a green sheet, but for forming a peeling layer, the printability to a PET film etc. falls and during printing or after drying, the peeling layer easily sheds ceramic powder and the effect of forming the peeling layer tends strongly to be impaired. Therefore, it was difficult to apply the technology of Japanese Patent No. 3367455 to a peeling layer paste for forming a peeling layer. On the other hand, if increasing the amount of binder to raise the concentration in the dispersion process, the dispersion overly rises in viscosity, so good dispersion is difficult. Therefore, it is necessary to provide a later dilution process, cause good dispersion in the state with a small amount of binder, and in the later dilution process add a binder to adjust the amount of the binder.